Speed reducer

ABSTRACT

A mechanical power transmission means in which there is a driving element, a driven element, and a shaft on which one of the elements is mounted. The shaft contains a chamber with a heat pipe system therein for transmitting heat generated in or transferred to the element on said shaft, to a point remote from the element for regulating the temperature in the power transmission means. The present concept is particularly adapted to speed reducers of the worm and gear type.

United States Patent 1191 Sharp Feb. 13, 1973 SPEED REDUCER [75]Inventor: Theo F. Sharp, South Bend, Ind.

[73] Assignee: Reliance Electric Mishawaka, Ind.

[22] Filed: Nov. 9, 1970 [21] Appl. No.: 87,703

Company,

[52] [1.8. CI. ..74/425, 165/47, 165/105 [51] Int. Cl ..F16h 1/16, F24h3/00, F28d 15/00 [58] Field of Search .....74/467, 425; 165/105, 47, 86

[56] References Cited UNITED STATES PATENTS 3,621,908 11/1971 Pravda..60/39.51 R 2,743,384 4/1956 Turner... ....165/105 UX 2,813,698 11/1957Lincoln ..1 65/105 X 3,151,669 10/1964 Quenneville l l ..l65/47 X3,229,759 1/1966 Grover ..165/105 3,481,439 12/1969 Finkin ..165/105X3,563,309 2/1971 Basiulis 3,595,304 7/1971 McHugh.....

3,605,878 9/1971 Coleman ..165/105 Primary Examiner-Leonard H. GerinAttorney-Hobbs & Green, Kemon, Palmer & Estabrook [57] ABSTRACT Amechanical power transmission means in which there is a driving element,a driven element, and a shaft on which one of the elements is mounted.The shaft contains a chamber with a heat pipe system therein fortransmitting heat generated in or transferred to the element on saidshaft, to a point remote from the element for regulating the temperaturein the power transmission means. The present concept is particularlyadapted to speed reducers of the worm and gear type.

15 Claims, 10 Drawing Figures PATENTEU FEB 1 3-1913- SHEET E OF 3INVENTOR. THEO E SHARP BY 7 *M ATTORNEYS SPEED REDUCER The operation ofspeed reducers of the worm and gear reduction type produces asubstantial amount of heat from the friction of the intermeshing gears,and this heat tends to build up as the operation continues,

resulting in over heating of the lubricating oil. As the oil becomeswarmer, its lubricating qualities diminish, thus creating furtherfrictional heat and a substantial rise in the temperature of thelubricant. In the past, excessive increases in temperature of the speedreducer gears and lubricant have been prevented or controlled by usingthe circulating lubricant to remove the heat from the gears, andthereafter cooling the lubricant by dissipating the heat through thegear reducer housing into the atmosphere. The housing is normallyprovided with fins on one or more areas to improve the efficiency ofheat transfer through the housing and the dissipation into the ambientair. This type of heat dissipating system had certain inherentdisadvantages, one of which has been the adverse effect of the heat onthe lubricant, which not only becomes less effective as a lubricantduring the critical operating periods of the reducers as a result of theincrease in temperature, but also decomposes or is otherwise permanentlyaltered so that frequent lubricant changes are necessary. It is,therefore, one of the principal objects of the present invention toprovide gear reduction units having a gear cooling system which removesthe heat from the gears before it has caused any appreciable increase inthe temperature of the lubricant in the unit, and which can beincorporated in most conventional or standard gear reduction unitswithout making any substantial changes or modification in the basicdesign thereof.

Another object of the invention is to provide a cooling system for thegears of a speed reducer which is incorporated in the shaft or hub ofone or more gears of the unit for removing the heat instantaneously fromthe gears as it is produced by the friction between the intermeshinggear teeth, thereby preventing the temperature of either the gears orthe lubricant from increasing to a point where the operation or functionof either will be impaired.

Still another object of the invention is to provide a relatively simple,highly efficient cooling system for gear reduction units whicheffectively protects the moving parts and the lubricant of the units,and which has no complicated parts or mechanisms likely to fail or wearexcessively over extended periods of operation of the gear reductionunits.

Another object is to provide a cooling system for the shafts of varioustypes of machinery having driving and driven elements, which iseconomical and efficient to operate, and which can be maintained inoptimum operating condition over long periods of time with a minimumamount of service. 7

Additional objects and advantages of the invention will become apparentfrom the following description and accompanying drawings, wherein:

FIG. 1 is an elevational and partial cross sectional view of a worm gearspeed reducer showing the worm in cross section;

,FIG. 2 is an elevational and partial cross sectional viewof anotherside of the reducer showing a portion of the worm gear in cross section;

FIG. 3 is an enlarged view of the worm'shaft showing in greater detailthe cooling mechanism embodied therein;

FIG. 4 is an enlarged cross sectional view of the worm shaft, thesection being taken on line 4-4 of FIG. 3; and

FIGS. 5 through 9 are diagrammatical views of various conditionsprevailing in speed reducer units, illustratin g the function andeffectiveness of the present improvement; and I FIG. 10 is a crosssectional view of a modified form.

The present invention is primarily concerned with the dissipation offriction generated heat from intermeshing gears, particularly in speedreducers of the worm and gear type, and involves the utilization of aheat pipe system incorporated in the rotating shaft of the worm. Aconventional worm gear speed reducer with self-contained oil lubricationhas a heat-flow or heat dissipation pattern given essentially by thethermal circuit shown in FIG. 5. The head generated in the gear is firsttransferred to the lubricating oil, which in turn heats the housing, andthe heat is dissipated from the housing surface to the ambient air byconventional modes, such as natural convection without a fan, or forcedconvection with a fan, augmented in some degree by radiation. Since thehighest temperature is at the gear, and since the thermal resistancesfrom the worm or gear to ambient air are essentially in series, thetemperatures are successively lower at the oil sump, housing, and theambient air. Under normal conditions the limiting temperature usuallyoccurs in the oil sump, in that when the oil temperature becomes toohigh, the oil deteriorates and loses its effective lubricatingproperties.

A heat pipe system, including wick type or rotating wickless typeutilized in the present concept, is an excellent heat conductor, itsthermal conductivity normally being many times greater than that forpure copper, and when incorporated in the shaft of a conventional wormgear speed reducer, greatly improves the performance of such a reducer.As used in the present concept, the heat pipe in its broadest senseconsists essentially of an evaporator where heat is absorbed, acondenser where heat is rejected, and'a means for transporting theliquid condensate from the condenser to the evaporator. The advantagesof the heat pipe in a speed reducer or similar mechanism is illustratedby the diagrams of FIG. 6 which compares the dissipation of heat from aspeed reducer with the heat pipe incorporated therein with thedissipation of heat from a conventional speed reducer. The heat pipesystem is not a substitute for the conventional heat dissipating system,but rather is in addition thereto, providing a second and superior pathof thermal flow from the gear and worm to ambient air, as illustrated bythe diagram of FIG. 7. It is seem that the heat pipe is represented by aparallel resistance, since it transmits part of the heat generationdirectly to the housing, leaving the rest to go through the usual route.The net effect of utilizing heat pipe is to reduce the temperature levelat the gear and in the oil. The reductions in temperature at thesecritical points improve the service life of the reducer.

The heat dissipating capacity of the present system is further improvedby connecting the reducer shaft directly to an external heat exchanger.An example of such an arrangement is shown in FIG. 8 wherein the coolantthrough the heat exchange may be either air, water or oil. The thermalcircuit for this configuration is depicted in FIG. 9. In view of the lowresistance of the heat pipe, most of the heat generated at the gear isdirectly dissipated in the heat exchanger, with a small portion goingthrough the usual route of oil, housing and ambient air. This design hasa much higher thermal capacity for given allowable gear and oiltemperatures, when compared with that of the conventional reducer.

Referring to the specific reducer embodiment illustrated in thedrawings, numeral 10 indicates generally the worm gear speed reducer, 12a worm shaft having threads 14 thereon and a cooling system or mechanism16 therein. Shaft 12 is driven by a gear, sheave or other drive elementmounted on or connected to shaft end 17, and worm threads 14 intermeshwith and drive a worm gear 18. A housing indicated generally by numeral20 encloses the worm and gear and is provided with a sump 22 for alubricant for the gears and shaft bearings. The worm thread may be ofany standard type, and hence is only shown in outline form in thedrawings. While the present cooling system 16 is shown in conjunctionwith a worm gear speed reducer, it can be used beneficially with othertypes of shafts for intermeshing gears where the friction produced heatfrom the intermeshing gears must be dissipated in order to obtainoptimum operating performance.

Worm 12 is journalled in bearings 30 and 32, which in turn are mountedin the housing in annular bosses 34 and 36, respectively, the annularbosses containing holes 38 and 40 which are closed by plates 42 and 44secured to the housing by a plurality of bolts 46 and 48. Worm gear 18is mounted on a shaft 49 journalled in bearings 50 and 52, which in turnare mounted in plates 54 and 56, respectively, disposed in housingopenings 58 and 60 and secured to the housing by a plurality of bolts 62and 64, respectively. The shaft for the worm gear is of the doubleoutput type having portions 66 and 68 at each end of the shaft forreceiving gears, sheaves or other drive elements. While a double outputshaft is shown, the reducer may instead have a single output shaft ifdesired. The housing is shown with a plurality of fins 70 on theexternal surface thereof for dissipating the heat transmitted throughthe adjacent housing sidewall from the lubricant in the housing duringthe operation of the reducer, although the necessity for the fins isminimized by the cooling system hereinafter described.

An impeller 80 mounted on the shaft of the worm for rotation therewithis used to circulate air around the housing and fins in order to provideeffective heat dissipation from the gear reducer. The impeller isenclosed in a shield 82 having an air intake 84 concentric with theshaft, and variousoutlet openings 86 around its periphery, which directthe air from the impeller to the various surfaces of the reducerhousing.

Since most of the heat generated by friction between the gears occursbetween the worm threads and the teeth of the worm gear, a heat pipesystem 88 is disposed in the center of the shaft 12 and extends axiallytherein from a position adjacent the threaded section of the worm, wherethe heat is absorbed, to one end of the shaft where the heat isdissipated into the ambient air, either directly or through a heatexchanger. The specific embodiment of the heat pipe shown in the drawingconsists of a closed evacuated chamber 90 in the shaft, closed at theleft hand end by threaded plug 92, and at the right hand end by a plug94 threaded into the otherwise open end of the shaft, the plugs formingeffective seals with the sides of the shaft so that chamber 90 willmaintain its evacuated condition for extended periods of operation.

The heat pipe shown is of the wick type, although a rotating wicklesstype is suitable for the present operation. In the one shown, capillarystructure or wick lines the wall of chamber 90, extending the fulllength thereof, and may consist of a variety of different materialscapable of producing an effective capillary action, examples of suchmaterials being fiber glass, woven mesh, or sintered porous matrices.The working fluid in the heat pipe may likewise be of a variety ofdifferent materials, consisting, for example, of methanol, acetone,water, and fluoridated hydrocarbons, which will readily vaporize withinthe temperature range normally encountered during the operating of thespeed reducer. While the shaft is shown in the drawings as forming thewalls of chamber 90, a separate container having side walls of a highheat conductivity material, such as copper or aluminum, may beconstructed separately and fitted snugly into the center bore of theshaft as a complete unit.

In the rotating-wickless or centrifugal embodiment, the return of thecondensate from the condenser to the evaporator is accomplished bycentrifugal action of a rotating shaft having an axial bore whichincreases in diameter from the condenser at the end of the shaft to theevaporator at the center, as illustrated diagrammatically in FIG. 10.The design of the wall of the bore causes the condensed fluid to movefromthe heat dissipating end to the heat absorbing end as the shaftrotates during operation of the speed reducer. In some installations,the embodiment involving the true capillary action may be preferred,since it not only functions effectively throughout the operatingof thereducer, but continues to function after the reducer has stoppedoperating to dissipate the residual heat in the gears and shaft.

In the operation of the heat pipe system, the heat generated by theoperation of the worm and worm gear is transmitted through the walls ofshaft 12 to the adjacent end of the heat pipe, where it heats theworking fluid in wick 100, causing the fluid to evaporate from the wickto increase the vapor pressure in the corresponding end of chamber 90.As a result, the vapor moves along the chamber carrying the heat energytoward the right hand end of the chamber, as viewed in the drawings,where the heat is dissipated through the side walls of the shaft andcarried away by the air circulated under cover 84 by the operation ofimpeller 80 and/or other suitable heat dissipating means such as fins.When the heat is removed from vapor in the right hand end of thechamber, the vapor condenses, entering wick 100, and returns in liquidform by capillary action to the inner end of the chamber 90. Thisoperational cycle of heat absorption and vaporization, and then heatdissipation and condensation, continues indefinitely withoutinterruption as long as there is a differential in temperature betweenthe gears and the heat dissipating means at the outer end of the shaft,thus providing optimum operating performance of the speed reducer andeffective protection to the unit.

While the present invention has been described with reference to a speedreducer, the broader concept includes transmission of heat from adriving or driven element through a shaft on which one of the elementsis mounted, to a dissipating point remote from the element. Variousshaft structures and designs and drive and driven elements thereon canbe effectively cooled by the present cooling system.

Although only one embodiment has been described, various changes andmodifications may be made without departing from the scope of theinvention.

I claim:

1. A speed reducer comprising a worm having a threaded portion thereon,a worm gear shaft having teeth intermeshing with the threads on saidworm and having a longitudinally arranged chamber therein extending froma point in close proximity to said threaded portion to a point remotetherefrom, a heat pipe system in said chamber having an evaporator endin close proximity to to said threaded portion and a condenser endremote therefrom and a fluid therein vaporized by the heat generated bythe intermeshing threads and teeth for transferring the heat to saidremote point, and a means for dissipating the heat from said remotepoint.

2. A speed reducer as defined in claim 1 in which a housing is providedfor said worm and gears and said shaft extends through the wall of saidhousing and a heat dissipating means is associated with the shaftexternally with respect to said housing.

3. A speed reducer as defined in claim 2 in which said heat dissipatingmeans includes an impeller mounted on said shaft for circulating airabout the shaft.

4. A speed reducer as defined in claim 1 in which the chamber includes acapillary active material extending substantially the full lengththereof.

5. A speed reducer as defined in claim 4 in which a capillary activematerial is selected from a group of materials including sintered porousmatrices, woven mesh, and fiber glass.

6. A speed reducer as defined in claim 5 in which said fluid is selectedfrom a group consisting of methanol, acetone, water and fluoridatedhydrocarbons.

7. A speed reducer as defined in claim 1 in which said fluid is selectedfrom a group consisting of methanol, acetone, water and fluoridatedhydrocarbons.

8. A speed reducer as defined in claim 1 in which said heatpipe systemis a wickless, rotating shaft type.

9. A speed reducer as defined in claim 1 in which said system includes abore in said shaft increasing in diameter from one end thereof towardsaid inner end of said chamber.

10. A mechanical power transmitting means including a driving elementand a driven element, a housing for said elements, a shaft rotatablysupporting one of said elements and extending through the wall of saidhousing, said shaft having a longitudinally arranged chamber thereinextending from a point in close proximity to said element to a pointremote therefrom, a

heat pipe system in said chamber havin an eyaporator end m closeproximity to said threade portion and a condenser end remote therefromand a fluid therein vaporized by heat transmitted from said element tosaid shaft for transferring the heat to said remote point and associatedwith said shaft for dissipating the heat from the shaft.

11. A mechanical power transmitting means as defined in claim 10 inwhich the chamber includes a capillary active material extendingsubstantially the full length thereof.

12. A mechanical power transmitting means as defined in claim 11 inwhich a capillary active material is-selected from a group of materialsincluding sintered porous matrices, woven mesh, and fiber glass.

13. A mechanical power transmitting means as defined in claim 12 inwhich said heat pipe includes a bore in said shaft decreasing indiameter toward an outside end thereof.

14. A mechanical power transmitting means as defined in claim 10 inwhich said fluid is selected from a group consisting of methanol,acetone, water and fluoridated hydrocarbons.

15. A mechanical power transmitting means as defined in claim 10 inwhich saidheat pipe system is a wickless, rotating shaft type.

1. A speed reducer comprising a worm having a threaded portion thereon,a worm gear shaft having teeth intermeshing with the threads on saidworm and having a longitudinally arranged chamber therein extending froma point in close proximity to said threaded portion to a point remotetherefrom, a heat pipe system in said chamber having an evaporator endin close proximity to to said threaded portion and a condenser endremote therefrom and a fluid therein vaporized by the heat generated bythe intermeshing threads and teeth for transferring the heat to saidremote point, and a means for dissipating the heat from said remotepoint.
 1. A speed reducer comprising a worm having a threaded portionthereon, a worm gear shaft having teeth intermeshing with the threads onsaid worm and having a longitudinally arranged chamber therein extendingfrom a point in close proximity to said threaded portion to a pointremote therefrom, a heat pipe system in said chamber having anevaporator end in close proximity to to said threaded portion and acondenser end remote therefrom and a fluid therein vaporized by the heatgenerated by the intermeshing threads and teeth for transferring theheat to said remote point, and a means for dissipating the heat fromsaid remote point.
 2. A speed reduCer as defined in claim 1 in which ahousing is provided for said worm and gears and said shaft extendsthrough the wall of said housing and a heat dissipating means isassociated with the shaft externally with respect to said housing.
 3. Aspeed reducer as defined in claim 2 in which said heat dissipating meansincludes an impeller mounted on said shaft for circulating air about theshaft.
 4. A speed reducer as defined in claim 1 in which the chamberincludes a capillary active material extending substantially the fulllength thereof.
 5. A speed reducer as defined in claim 4 in which acapillary active material is selected from a group of materialsincluding sintered porous matrices, woven mesh, and fiber glass.
 6. Aspeed reducer as defined in claim 5 in which said fluid is selected froma group consisting of methanol, acetone, water and fluoridatedhydrocarbons.
 7. A speed reducer as defined in claim 1 in which saidfluid is selected from a group consisting of methanol, acetone, waterand fluoridated hydrocarbons.
 8. A speed reducer as defined in claim 1in which said heatpipe system is a wickless, rotating shaft type.
 9. Aspeed reducer as defined in claim 1 in which said system includes a borein said shaft increasing in diameter from one end thereof toward saidinner end of said chamber.
 10. A mechanical power transmitting meansincluding a driving element and a driven element, a housing for saidelements, a shaft rotatably supporting one of said elements andextending through the wall of said housing, said shaft having alongitudinally arranged chamber therein extending from a point in closeproximity to said element to a point remote therefrom, a heat pipesystem in said chamber having an evaporator end in close proximity tosaid threaded portion and a condenser end remote therefrom and a fluidtherein vaporized by heat transmitted from said element to said shaftfor transferring the heat to said remote point and associated with saidshaft for dissipating the heat from the shaft.
 11. A mechanical powertransmitting means as defined in claim 10 in which the chamber includesa capillary active material extending substantially the full lengththereof.
 12. A mechanical power transmitting means as defined in claim11 in which a capillary active material is selected from a group ofmaterials including sintered porous matrices, woven mesh, and fiberglass.
 13. A mechanical power transmitting means as defined in claim 12in which said heat pipe includes a bore in said shaft decreasing indiameter toward an outside end thereof.
 14. A mechanical powertransmitting means as defined in claim 10 in which said fluid isselected from a group consisting of methanol, acetone, water andfluoridated hydrocarbons.